The invention relates to a photomultiplier tube comprising a sealed envelope having a longitudinal axis of symmetry, which tube is radially segmented into N segments which are disposed at regular intervals around said longitudinal axis, each segment having an elementary photomultiplier, said tube comprising, more specifically, a photocathode arranged on the inner surface of the faceplate of the envelope, which is transparent to light, an electron multiplier of the leaf type which is arranged so as to have N multiplication paths which correspond to N elementary photomultipliers, and further comprising an electron-optical device which ensures that the photoelectrons are divided in N multiplication paths, depending on the position of the photoelectrons when they leave the photocathode.
A photomultiplier of this type is known from EP-A-428215(which corresponds to U.S. Pat. No. 5,126,629). According to said document, the aim is to provide, more specifically, a category of photomultipliers having a small number of N paths and which can be produced in a simple manner and at low cost.
A typical application of this type of photomultiplier consists in assembling a plurality of tubes into a mosaic in order to determine the positions in space of localized luminous phenomena, originating, for example, from scintillators placed in front of each tube. By using segmented photomultiplier tubes whose construction is not very complicated and, hence, relatively cheap, substantial economies can be realised in the manufacture of such an analysis mosaic. To ensure a satisfactory measuring accuracy, the different elementary photomultipliers used to assemble each segmented tube must exhibit minimal differences in performance between the tubes and the segments while also avoid crosstalk between the paths of one single tube.
The requirement of constructional simplicity is met, to a certain degree, by the segmented tube known from the above-mentioned document, i.e. the electron beam issuing from the photocathode is divided in N different paths, depending on the position of the electrons when they leave the photocathode; said division not being realised by physical means, such as partitions, but rather by an adequate distribution of the electric field. The majority of the electrodes used in said tube have different paths in common, which leads to a very simple construction.